RFmx Power Different from VRTS Trigger Power Level

Updated May 19, 2020

Reported In

Software

  • RFmx

Driver

  • NI-VRTS

Issue Details

I'm using NI VRTS and RFmx and have an IQ Power trigger configured for my acquisition. When the trigger goes off, my power data returned by RFmx does not match the IQ Power trigger level I set; e.g. if I set an IQ Power trigger threshold of 35 dBm, it will trigger but my RFmx power trace will show a lower power such as 10 dBm. Why does this happen?

Solution

When you configure an IQ Power trigger with the NI VRTS API, the power will always be read across the entire configured VRTS bandwidth. If the RFmx measurements are not configured for the same bandwidth, then the power measured will differ. For example, if the RFmx measurement spans a much smaller bandwidth than the VRTS configuration, the RFmx measurement will capture less total power. 

Configure RFmx to match the bandwidth of the VRTS acquisition to ensure the measured power is the same.